Heat treatment apparatus

ABSTRACT

A heat treatment apparatus is provided which includes heating means for enabling a rapid temperature rise to a temperature of 1600 through 1900° C., and a thermometer capable of accurately measuring temperatures even when rapid temperature rises and drops are repeated, the heat treatment apparatus being capable of performing heat treatment of an SiC substrate with good mass productivity after ion implantation. The heat treatment apparatus enables the heat treatment of a semiconductor substrate at 1600 to 1900° C. by temperature control using a resistance heating element and thermocouple thermometers. The heat treatment apparatus is configured such that the resistance heating element and the thermocouple thermometers include a common constituent metal as a main component.

This is a Continuation of U.S. application Ser. No. 14/236,161 filedJan. 30, 2014, which is a National Stage of International ApplicationNo. PCT/JP2011/068100 filed Aug. 9, 2011. The disclosures of the priorapplications are hereby incorporated by reference herein in theirentireties.

TECHNICAL FIELD

The present invention relates to a heat treatment apparatus which isuseful for the heat treatment of an SiC substrate after ionimplantation.

BACKGROUND ART

The activation heat treatment of an SiC substrate after ion implantationrequires a temperature from 1600 to 1900° C. It is also required toperform the activation heat heat treatment in a short period of time inorder to activate impurities without imparting time for atoms to move.It is further required to reduce variations in the in-plane temperaturedistribution of the SiC substrate being heat treated as well as toprovide improved mass productivity.

In response to such a demand, a heat treatment apparatus has beensuggested in which a substrate was retained in a tube-shaped body formedof a high melting point material, and the tube-shaped body was heatedwith an RF coil at a high frequency to thereby create a high-temperatureregion in the tube-shaped body (Patent Literature 1). The heat treatmentapparatus provides a temperature rise rate of about 20 to 30° C. perminute which is two to three times that provided by heating using aconventional infrared lamp, thereby reducing variations in the in-planetemperature distribution.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-Open No.    2003-77855

SUMMARY OF INVENTION Technical Problem

However, the aforementioned heat treatment apparatus that employshigh-frequency heating is reduced in mass productivity of substrates tobe treated because the structure of a jig for retaining the substrate ina high-temperature region restricts the number of substrates to be heattreated at a time to 4 to 8.

Furthermore, the heat treatment apparatus has conventionally oftenprovided temperature control by measuring the temperature of thesubstrate with a radiation thermometer. However, the radiationthermometer requires a complicated procedure of determining acalibration curve by another temperature measurement method because theemissivity of thermal radiation differs depending on the substance to bemeasured. Furthermore, the radiation thermometer is significantlyinfluenced by the surface state of an object being measured, andaccurately measures temperatures with difficulty even due to soil on themeasurement port.

In response to this, it is conceivable to use a thermocouple thermometerin place of the radiation thermometer. However, use of the thermocouplethermometer in the high-frequency heating apparatus may lead toinaccurate temperature measurement due to self-heating or noise causedby induction. In this context, the heating method may be changed fromthe high-frequency heating to resistance heating. In this case, theproblem of the self-heating can be resolved. However, the activationheat treatment after ion implantation leads to high temperature rise anddrop rates, so that for example, use of the thermocouple thermometerincorporating an iridium rhodium alloy with a ceramic heater serving asheating means would cause the thermocouple to be worn and have a breakdue to grain boundaries.

In view of the aforementioned problems associated with the conventionaltechniques, an object of the present invention is to provide a heattreatment apparatus which includes: heating means enabling a rapidtemperature rise to a temperature of 1600 through 1900° C.; and athermometer which can measure temperatures with accuracy even when atemperature rise and a temperature drop are rapidly repeated, and whichis capable of heat treating a large number of substrates at a time andperforming heat treatment on an SiC substrate with improved massproductivity after ion implantation.

Solution to Problem

The present inventor has found that when employing resistance heating asthe heating method for a heat treatment apparatus and a thermocouplethermometer for temperature control, a heat treatment apparatus isconfigured to utilize a heating element responsible for the resistanceheating and the thermocouple each being formed of a common maincomponent metal, so as to provide a common atmosphere suitable for both.This can configure the heat treatment apparatus which is capable ofmaintaining accurate heat control due to optimum heat treatmentconditions being readily set even when abrupt increases and drops intemperature are repeated.

That is, the present invention provides a heat treatment apparatus for asemiconductor substrate, in which heat treatment can be performed at1600 to 1900° C. by temperature control using a resistance heatingelement and a thermocouple thermometer, wherein the resistance heatingelement and the thermocouple thermometer include a common constituentmetal as a main component.

Advantageous Effects of Invention

The heat treatment apparatus according to the present invention employsa resistance heating element for performing resistance heating and athermocouple thermometer formed of a main component common to that ofthe resistance heating element so as to provide temperature control tothe heat treatment of a substrate. This makes it possible to provide arapid temperature rise to a temperature of 1600 through 1900° C. as wellas to provide accurate temperature control to heat treatment even in thepresence of repeated rapid rises and drops in temperature. Thus, theheat treatment of an SiC substrate after ion implantation can be carriedout in an improved manner.

In addition, since a few tens of substrates can be heat treated at atime, the heat treatment of substrates can be performed with good massproductivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view illustrating a heat treatmentapparatus according to an embodiment.

FIG. 2 is across-sectional view, taken along X-X, illustrating the heattreatment apparatus according to the embodiment.

FIG. 3 is a view illustrating a change in heat treatment temperature.

DESCRIPTION OF EMBODIMENTS

Now, referring to the drawings, the present invention will be describedmore specifically.

FIG. 1 is a longitudinal sectional view illustrating a heat treatmentapparatus 1 according to an embodiment of the present invention, andFIG. 2 is across-sectional view taken along X-X.

This heat treatment apparatus 1 activates an SiC substrate 2 after ionimplantation and includes: a vertical type boat 3 which can accommodate20 or more SiC substrates 2 at the same time; a tube type container(hereafter to be referred to as the SiC tube) 4 formed of a high meltingpoint material (for example, SiC); a transfer device 6 for inserting ordrawing out the boat 3 into a heating chamber 5 formed in an upperregion within the SiC tube 4; a resistance heating element 7 disposed ina tubular shape so as to surround the heating chamber 5; a firstthermocouple thermometer 8 a with an end disposed between the resistanceheating element 7 and the SiC tube 4; and a second thermocouplethermometer 8 b with an end disposed in the heating chamber 5. The outerside of the resistance heating element 7 disposed in a tubular shape issurrounded by a reflector 11 formed from a tungsten and molybdenumalloy.

More specifically, the resistance heating element 7 is made up of threeplate type heating elements that are each bent to form three planes, sothat these three bent plate type heating elements 7 a, 7 b, and 7 c areformed in a tubular shape to surround the outer periphery of the SiCtube 4 that forms the heating chamber 5. In this case, as shown in FIG.2, the tube-shaped body is an approximately regular dodecagon in crosssection, and the three bent plate type heating elements 7 a, 7 b, and 7c occupy nine sides of the generally regular dodecagon. Also providedare three heater electrodes 9 and guide pipes 10 corresponding to therespective three bent plate type heating elements 7 a, 7 b, and 7 c. Asillustrated by FIGS. 1 and 2, each bent plate type heating element 7 a,7 b, and 7 c includes a top surface 71, a bottom surface 72 and a singlecontinuous side surface 73, the single continuous side surface 73 havinga plurality of bent planes 73 p, 73 q, and 73 r with each plane 73 p, 73q, and 73 r of the side surface 73 intersecting each other and eachplane 73 p, 73 q, and 73 r extends between the top surface 71 and thebottom surface 72.

To dispose a plurality of plate type heating elements in a tubularshape, the heating elements preferably form a circle in cross sectionfrom the viewpoint of the thermal uniformity in the cross section of theheating chamber 5. However, plate type heating elements may be disposedso as to form a regular polygon with six sides or more, for example,around the SiC tube 4 having an outer diameter of 145 mm or more, morepreferably 145 to 185 mm, thereby ensuring a sufficient thermaluniformity in the cross section.

On the other hand, in disposing a plurality of plate type heatingelements in a tubular shape, the entire periphery is not always requiredto be occupied with the heating elements, so that the individual platetype heating elements may be disposed with a gap therebetween. However,when there are too many regions in which no heating element exists, thetemperature of the heating chamber 5 cannot be rapidly increased to 1600through 1900° C. Thus, for example, in employing a plurality of platetype heating elements to form a regular polygon with 12 or more sides,it is preferable to occupy ¾ the number of sides or greater with theheating elements. Thus, the resistance heating element 7 of thisembodiment which employs the three bent plate type heating elements 7 a,7 b, and 7 c, each having three continuous rectangular planes, so as toform a generally regular dodecagon provides the heating chamber 5 withan improved thermal uniformity. In other words, as illustrated by FIGS.1 and 2, the side surfaces 73 collectively form an approximately tubularpolygonal shape in cross section in which each plane 73 p, 73 q, and 73r faces a center of the approximately tubular polygonal shape where theheating chamber 5 is located and a periphery of the approximatelytubular polygonal shape includes the plurality of metal heating elements7 a, 7 b, and 7 c disposed with a gap between adjacent metal heatingelements 7 a, 7 b, and 7 c.

On the other hand, in disposing plate type heating elements so that theheating elements form a tubular polygonal shape in cross section, bentplate type heating elements each having a plurality of adjacent planes,more preferably two to four continuous side surfaces, may be morepreferably used because the total number of heating elements can bereduced and the manufacturing costs of heating elements can also bereduced. That is, the side surfaces collectively form an approximatelytubular polygonal shape in cross section in which a periphery of theapproximately tubular polygonal shape includes the plurality of metalheating elements disposed with a gap between adjacent metal heatingelements. In this context, although a resistance heating element whichis made of tungsten and formed cylindrically in a mesh is conventionallyknown, bent plate type heating elements can be disposed in a tubularshape as a heating element as in this embodiment, thereby reducing theprocessing costs of the heating element by 15 to 20%.

Note that rod-shaped heating elements may also be conceivably disposedin a tubular shape in place of the plate type heating elements, but maylead to an increase in the number of electrodes, thus unpreferablymaking the processing of the mantle and the structure of the heatingchamber 5 complicated.

On the other hand, as the first thermocouple thermometer 8 a and thesecond thermocouple thermometer 8 b, the heat treatment apparatus 1includes a tungsten rhenium alloy thermocouple (rhenium 5%, 26%) whichhas a main component common to that of the aforementioned plate typeheating elements 7 a, 7 b, and 7 c. Thus, the heat treatment apparatus 1can be used at a high temperature in a reduction atmosphere.Furthermore, the heat treatment apparatus 1 can maintain a heatingaccuracy within ±1° C. with respect to 1900° C. even when heattreatments are repeated because heating control is performed not byhigh-frequency heating but by resistance heating and a thermocouplethermometer. Heating the heating chamber by a conventional combinationof the high-frequency heating and the radiation thermometer may cause anerror of about ±10° C. It can be thus seen that the heat treatmentapparatus 1 of this embodiment provides a significantly improvedtemperature control accuracy.

As atmosphere control means, the heat treatment apparatus 1 has a gasinlet pipe 12 for drawing an inert gas such as argon or nitrogen intothe SiC tube 4 that forms the heating chamber 5, and a gas dischargepipe 13 for discharging the gas from the SiC tube 4. The lower end ofthe SiC tube 4 is closed with a quartz plate 16 via an O-ring 15. Notethat dummy plates 14 are placed at a lower portion of the heatingchamber 5 inside the SiC tube 4 to thermally insulate the heatingchamber 5, and a farther lower region is surrounded by a sub-chamber 17through which water is passed to cool down the SiC tube 4. Furthermore,a stainless steel water cooling pipe 18 is provided outside thereflector 11.

The heat treatment apparatus 1 is used as follows.

At a temperature of 300° C. or lower in the heating chamber 5, asubstrate 2 placed on the boat 3 is inserted into the heating chamber 5by actuating the transfer device 6, an inert gas such as argon is drawnfrom the upper end of the SiC tube 4 through the gas inlet pipe 12, andoxygen and water are discharged from the lower end of the SiC tube 4through the gas discharge pipe 13. Then, the resistance heating element7 is used to rapidly heat the heating chamber 5 to a temperature of1600° C. or higher, heat treatment is completed in a few minutes, andthe heating chamber 5 is then cooled down. FIG. 3 shows an example ofchanges in temperature inside and outside the heating chamber 5 for thiscase. As can be seen, the heating apparatus enables a rapid temperaturerise at a rate of 100° C. or greater per minute, and preferably at arate of 200° C. or greater per minute. It is thus possible to performthermal activation treatment after ion implantation without diffusingimpurities in the substrate.

REFERENCE SIGNS LIST

-   -   1 Heat treatment apparatus    -   2 Substrate    -   3 Boat    -   4 SiC tube    -   5 Heating chamber    -   6 Transfer device    -   7 Resistance heating element    -   7 a, 7 b, 7 c Plate type heating element    -   8 a, 8 b Thermocouple thermometer    -   9 Heater electrode    -   10 Heater electrode guide pipe    -   11 Reflector    -   12 Gas inlet pipe    -   13 Gas discharge pipe    -   14 Dummy plate    -   15 O-ring    -   16 Quartz plate    -   17 Sub-chamber    -   18 Water cooling pipe

1. A heat treatment apparatus for a semiconductor substrate, in whichheat treatment can be performed at 1600 to 1900° C. by temperaturecontrol using a resistance heating element and a thermocouplethermometer, wherein: the resistance heating element and thethermocouple thermometer include a common constituent metal as a maincomponent, the resistance heating element includes a plurality of bentplate type metal heating elements, each metal heating element includestwo to four continuous side surfaces, and the side surfaces collectivelyform an approximately tubular polygonal shape in cross section in whicha periphery of the approximately tubular polygonal shape includes theplurality of metal heating elements disposed with a gap between adjacentmetal heating elements and in the cross section each metal heatingelement includes two to four bent planes.
 2. The heat treatmentapparatus according to claim 1, wherein the heat treatment apparatusenables a temperature rise of 100° C. or greater per minute.
 3. The heattreatment apparatus according to claim 1, comprising a heating chamberformed of a high melting point material, the heating chamber disposedinside the metal heating elements.
 4. The heat treatment apparatusaccording to claim 3, wherein the metal heating elements have three sidesurfaces.
 5. The heat treatment apparatus according to claim 3, whereinthe heating chamber is formed of a SiC tube.
 6. The heat treatmentapparatus according to claim 2, comprising a heating chamber formed of ahigh melting point material, the heating chamber disposed inside themetal heating elements.
 7. The heat treatment apparatus according toclaim 6, wherein the metal heating elements have three side surfaces. 8.The heat treatment apparatus according to claim 6, wherein the heatingchamber is formed of a SiC tube.
 9. The heat treatment apparatusaccording to claim 1, wherein each plane of the two to four bent planesintersects each other and each plane extends between a top surface and abottom surface of each metal heating element.
 10. The heat treatmentapparatus according to claim 1, wherein: each metal heating elementincludes a top surface, a bottom surface and the two to four continuousside surfaces, and the two to four continuous side surfaces form asingle continuous surface having the two to four bent planes thatintersect each other and that extend between the top surface and thebottom surface.
 11. The heat treatment apparatus according to claim 10,wherein: the side surfaces collectively form the approximately tubularpolygonal shape in cross section in which each plane of the two to fourbent planes faces a center of the approximately tubular polygonal shape.